Statistical Mechanics
Observation of universal hierarchical relaxation in a quantum simulator
Jiaozi Wang, Manoj K. Joshi, Luca Capizzi et al. (+4 more)
Autocorrelation functions play a key role in the theoretical characterization of the dynamical properties of interacting many-body
quantum systems. Recently, bringing together the eigenstate thermalization hypothesis and hydrodynamics, it was theoretically predicted that the relaxation of autocorrelators can be described by the relaxation-overlap inequality, which, when saturated, predicts a hierarchy of relaxation exponents for a set of operators that are easily identified and constructed. Here, we employ a trapped-ion
quantum simulator to experimentally demonstrate it in the diffusive regime; to do so, we have extended the theory of the overlap-relaxation inequality to systems with multiple conservation laws. Our study thus opens the path to a thorough characterization of the relaxation to
equilibrium and appearance of hydrodynamic behavior in
quantum matter.
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All authors Jiaozi Wang, Manoj K. Joshi, Luca Capizzi, Rainer Blatt, Christian F. Roos, Leonardo Mazza, Dario Poletti
Materials Science
Radiation-technological processes under intense irradiation of a complex fractal medium
Zatsepin Anatoly Fedorovich, Oksengendler Boris Leonidovich, Suleymanov Sultan Khamidovich et al. (+2 more)
A fracton model of a complex medium has been constructed to study physicochemical processes for radiation-technological purposes that occur under intense irradiation. The possibility of shock-wave generation, as well as of percolation phenomena involving fractal aggregates, has been studied in the search for an ideal thermal
insulator.
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All authors Zatsepin Anatoly Fedorovich, Oksengendler Boris Leonidovich, Suleymanov Sultan Khamidovich, Ibrokhimov Rakhmatullo, Nigora Turaeva
Materials Science · Cross-listed from physics.hist-ph
Piezoelectricity: A Brief History of its Discovery and Physical Principles Using the Example of Low Quartz
Ruediger G. Ballas and Nataliya Koev
Piezoelectricity is a key phenomenon in solid-state physics and has significant technological relevance. In teaching, however, it is often treated either without a historical context or an explicit link to the microscopic
crystal structure, meaning that a crucial level of understanding remains untapped. This study combines the history of the discovery of piezoelectricity with its physical description within a didactically coherent framework. Building on the work of the brothers, Jacques and Pierre Curie (1880 - 1882), it demonstrated how investigations into pyroelectricity led to the identification of polarization induced by mechanical compression in hemihedral
crystals such as tourmaline and quartz. The development from early qualitative experiments towards the first quantitative determination of piezoelectric constants is traced in a structured manner. Using low quartz as an example, the microscopic cause of piezoelectricity was attributed to the asymmetric displacements of silicon and oxygen ions within the orthosilicate ion tetrahedral network. This leads to the formation of macroscopic polarization owing to uncompensated dipole moments in the
crystal lattice. The direct and reciprocal piezoelectric effects are qualitatively distinguished and discussed in the context of mechanical-electrical coupling. The article is aimed at students in physics and engineering as well as lecturers. It was conceived as a didactic review article (tutorial article) and serves as a structured introduction to the physical and historical foundations of piezoelectricity.
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Materials Science
Anisotropic Magnetic and Transport Properties of RAlGe (R = Y, Gd-Tm, Lu)
Tyler J. Slade, Lin-Lin Wang, Sergey L. Bud'ko et al. (+1 more)
We grew single
crystals of the RAlGe family for R = Y, Gd-Tm, Lu and characterized them with powder X-ray diffraction, temperature dependent specific heat measurements as well as temperature and field dependent resistance and magnetization measurements. These RAlGe materials crystallize in an orthorhombic Cmcm
crystal structure in which the R atoms occupy a position with $m$2$m$ point
symmetry. We find that when R is a moment bearing rare earth atom, the RAlGe materials order antifferomagnetically at $T_{\text{N}}$ ranging from 5 K (TmAlGe) to 39 K (TbAlGe). A second, lower temperature antiferromagnetic transition is also detected in the range 6-8 K for R = Tb-Ho, but no lower transition is observed (for T above 1.8 K) for R = Er, Tm. The R = Tb-Tm members show evidence for strong
crystal field effects influencing the physical properties, where the
crystal field favors an easy $a$-axis for R = Tb-Ho and an easy $b$-axis for R = Er, Tm. Of these compounds, strongly uniaxial behavior is observed for DyAlGe and TmAlGe. At T = 2 K, rich metamagnetism is observed when the external field is applied along the $a$-axis for R = Tb–Ho, whereas a single metamagnetic transition is observed (up to 70 kOe) with the field along the $b$-axis when R = Er and Tm. All RAlGe materials show metallic transport behavior and have moderate positive magnetoresistance up to 60-150 % at 2 K superimposed on top of metamagnetic features. The field dependent magnetization measurements on non-moment bearing YAlGe show clear de Haas-van Alphen oscillations, indicating the Fermi surface includes small, high mobility pockets.
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All authors Tyler J. Slade, Lin-Lin Wang, Sergey L. Bud'ko, Paul C. Canfield
Materials Science
Unified description of exciton, phonon and plasmon dispersions in 2D materials from an optical conductivity approximation
Alberto Guandalini, Andrea Ferretti, Daniele Varsano et al. (+2 more)
The modified Coulomb interaction in two-dimensional (2D) materials gives rise to unique, non-analytic low-momentum dispersions of
excitons,
phonons, and plasmons. Here, we describe the 2D dispersion of longitudinal excitations by introducing the optical conductivity approximation (OCA), a unified framework that evaluates the finite-q longitudinal response probed by electron energy-loss spectroscopy (q-EELS) by only using the q = 0 optical conductivity. By doing so, the approach demonstrates that the linear dispersion of all the above mentioned excitations is mainly due to the form of the 2D macroscopic Coulomb interaction rather than to the dispersion of the underlying band structure. Applying this approach to hexagonal boron nitride and
graphene we accurately reproduce the energy and intensity dispersions of the hBN longitudinal-optical
phonon and low-energy bright
excitons, along with the
graphene pi-plasmon. Our work also provides an efficient computational scheme to describe low momentum EELS data without the need to calculate the response functions at dense moment
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All authors Alberto Guandalini, Andrea Ferretti, Daniele Varsano, Paolo Barone, Francesco Mauri
Quantum Gases
Microscopic theory of the collective optical response of dilute atomic clouds at finite temperature
Tanja Schoger, Romain Pierrat and Nicolas Cherroret
At low temperature, collective light-induced dipole-dipole interactions are known to strongly reshape the optical response of atomic clouds, revealing the breakdown of the independent-scattering picture as the density increases. While thermal motion is generally believed to progressively suppress these interactions, the microscopic mechanisms behind this suppression remain largely unexplored. Here, we develop a microscopic theory of the optical response of a dilute atomic gas at finite temperature, explicitly accounting for atomic ballistic motion during the recurrent-scattering events associated with the collective corrections. Using a diagrammatic approach for scalar light, we derive the collective contribution to the optical permittivity and characterize its behavior across the full temperature range. We find that thermal corrections scale as $\sim T$ at low temperature, while recurrent-scattering contributions are suppressed as $\sim T^{-3/2}$ at high temperature. Our predictions are confirmed by extensive coupled-dipole simulations that explicitly account for atomic motion. These simulations also reveal the inaccuracy of the modified frozen-dipole approximation commonly used to treat thermal effects. Finally, extending our theory to vector light, we provide a complete picture of how the resonance shift continuously evolves from the collective Lamb shift at low temperatures to the classical Lorentz-Lorenz shift at high temperatures.
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Materials Science
X2SBench: an open benchmark for evaluating crystal structure determination from powder diffraction
Zhiyuan Gao, Juncheng Xiao, Shuchen Pu et al. (+7 more)
Progress towards practical powder X-ray diffraction (PXRD) structure determination requires evaluation beyond small
crystals and idealized patterns. X2SBench combines 152,587 simulated structure-pattern pairs with 591 curated measurements, extending evaluation to larger
cells, lower-
symmetry structures and diverse compositions. Fixed splits, defined inputs and common structural metrics support comparisons by
crystal system, atom count and element count. Joint stratification locates weaknesses within these groups. On 558 paired targets, an X2SBench-fine-tuned model improves recovery from simulated patterns but loses accuracy on measured inputs, revealing a gap in experimental transfer. Background subtraction and smoothing improve recovery for one tested checkpoint, while augmentation and reference-
lattice comparisons identify further opportunities for measurement adaptation and reliable
cell estimation. An open platform provides data access and standardized result submission, establishing a shared basis for community evaluation and progress towards practical PXRD analysis.
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All authors Zhiyuan Gao, Juncheng Xiao, Shuchen Pu, Qi Li, Weida Wang, Shufei Zhang, Yong Yang, Shifeng Jin, Yunqi Cai, Hongming Weng
Strongly Correlated Electrons
Exact phase diagram of the XXZ Heisenberg chain in a staggered magnetic field
H. P. Zhang and Z. Song
We study the phase diagram of the
spin-1/2 XXZ Heisenberg chain in a staggered
magnetic field. An exact solution is obtained along the phase boundary, where the exchange anisotropy and the staggered-field strength satisfy an exact analytical relation, yielding a highly degenerate
manifold of ground states with off-diagonal long-range order. We demonstrate that these exact ground states lie on the boundary between the ferromagnetic phase and a gapless Luttinger
liquid phase. Upon further decreasing the anisotropy, the gapless phase eventually gives way to a gapped
quantum-disordered phase. Large-scale density-
matrix renormalization group calculations confirm this phase structure and indicate that the transition across the exact boundary is of first order. Our results provide an exact
benchmark for understanding
quantum phase transitions driven by staggered
magnetic fields in one-dimensional
quantum spin systems.
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Mesoscale and Nanoscale Physics
Cavity-waveguide coupling in phononic crystals
Jakub Rosiński, Benjamin Mayer, Hubert J. Krenner et al. (+1 more)
Phononic
crystal platforms provide a promising route toward scalable on-chip
quantum networks, where mechanical excitations mediate interactions between solid-state
qubits. A key building block of such architectures is the cavity-waveguide system, in which localized mechanical modes couple to propagating phononic modes. However, a quantitative understanding of the mechanisms governing this coupling remains incomplete. In this work, we investigate the interaction between localized modes of snowflake-type phononic
crystal cavities and a phononic
crystal waveguide using finite-element simulations and experimental measurements. We show that the coupling strength is primarily governed by the spatial overlap between the displacement fields of the corresponding isolated cavity and waveguide modes. After accounting for the effective-mass dependence of the normalized cavity displacement amplitude, we establish a strong correlation between the spatial overlap and the interaction strength across a wide range of mode combinations. Deviations from this leading-order behavior are associated with Bloch-phase effects, variations in waveguide group velocity, and intrinsic hybridization of waveguide modes. Furthermore, we provide experimental evidence for cavity-waveguide coupling in a GaAs phononic
crystal membrane by observing a clear resonance in the spectral broadening of the photoluminescence emission from an embedded
quantum dot, which serves as a local probe of the mechanical field. The observed resonance at approximately 398 MHz is in good agreement with the corresponding cavity resonance near 395 MHz predicted by finite-element simulations. Our results identify spatial mode overlap as a leading-order design parameter for cavity-waveguide coupling and provide practical guidelines for controlling interactions between localized and propagating modes in phononic
crystal structures.
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All authors Jakub Rosiński, Benjamin Mayer, Hubert J. Krenner, Paweł Machnikowski
Soft Condensed Matter
Microscopic origin of the Baumgärtel-Schausberger-Winter Relaxation Spectrum in Polymer Melts and Particle Rafts
Dario Nichetti, H. Henning Winter and Alessio Zaccone
Entangled
polymer melts exhibit the robust two-branch Baumgärtel-Schausberger-Winter (BSW) relaxation spectrum, while related spectra occur in nonpolymeric monodisperse disordered systems. In spite of the successful application of BSW to many different materials, a molecular derivation of these spectra is lacking. We construct a molecular theory in which a chain segment moves relative to a screened, dynamically responding multichain environment. Gaussian-chain preaveraging gives $M_{\rm seg}(\Delta m)\sim(\Delta m)^{-1/2}$, hence $\lambda_p\sim p^{3/2}$ and, after stress projection, $H(\tau)\sim\tau^{-2/3}$. Independently, longitudinal primitive-path
diffusion gives contour-length fluctuations with $H(\tau)\sim\tau^{1/4}$. A molecular-weight-constrained implementation is tested simultaneously against experimental $G'(\omega)$ and $G''(\omega)$ data for four monodisperse polybutadiene (PBD) melts, without fitting spectral exponents or individual modal weights. The resulting BSW spectrum exhibits a continuous transfer from the fast cooperative to the slow constraint-renewal cascade before a finite-chain terminal edge. A common two-sector caged dynamics then connects
polymers to particle rafts without assuming identical microscopic mechanisms.
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Mesoscale and Nanoscale Physics
Nodal-Line Semimetals with Non-Quantized Berry Phase
Zhi-Xia Li, Liangliang Huang, Min-Xue Yang et al. (+3 more)
Nodal-line semimetals (NLSMs) are topological materials characterized by one-dimensional band crossings in momentum space, which typically carry a Berry phase quantized to integer multiples of $\pi$. Here, we extend the conventional paradigm to a class of NLSMs in which the Berry phase can take arbitrary fractional or even irrational multiples of $\pi$. This non-quantized Berry phase leads to a splitting of Landau levels when a
magnetic field is applied parallel to the nodal ring, an effect that can be detected via Shubnikov-de Haas oscillations in the magnetoconductivity. Despite the absence of a quantized topological invariant, drumhead-like surface states with weak dispersion persist at open boundaries. Notably, two identical surface states localize on the same boundary, in contrast to conventional NLSMs, where they reside on opposite boundaries. A systematic
symmetry analysis shows that such NLSMs can be realized in a broad range of
magnetic space groups. Our work opens a new avenue for exploring NLSMs beyond the conventional framework of a quantized Berry phase.
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All authors Zhi-Xia Li, Liangliang Huang, Min-Xue Yang, Feng Tang, D. Y. Xing, Wei Chen
Materials Science
Selective strain tuning of nonequilibrium multiferroic dynamics in BiFeO$_\text3$
Chenhang Xu, Patrick Liu, Bo Zhang et al. (+11 more)
Quantum materials are characterized by intertwined orders, and a fundamental goal in condensed matter physics is to achieve their selective control in such a way that one order parameter can be tuned while leaving others largely unaffected. Although significant progress has been made in thermal
equilibrium, realizing such control out of
equilibrium remains highly challenging. Here we employed in-situ tensile strain to selectively manipulate the photoinduced
lattice dynamics associated with ferroelectric and
magnetic orders in multiferroic BiFeO$_3$. By applying MeV ultrafast electron diffraction to freestanding BiFeO$_3$ membranes under tunable strain, we showed that tensile strain markedly suppresses the ultrafast photoinduced reduction of the ferroelectric displacement. By contrast, the photoinduced dynamics of the antiferrodistortive rotation of the oxygen octahedra, which modulates the
magnetic order, remains insensitive to strain. Not only do these findings reveal distinct microscopic pathways underlying nonequilibrium multiferroic dynamics, they also establish tunable strain as an effective route for engineering ultrafast phase control in correlated materials.
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All authors Chenhang Xu, Patrick Liu, Bo Zhang, Minyong Han, Henry G. Bell, Cameron J. R. Duncan, Yusong Liu, Patrick L. Kramer, Randy Lemons, Jake D. Koralek, Alexander H. Reid, Dong Qian, Harold Y. Hwang, Alfred Zong
Mesoscale and Nanoscale Physics
Library of carbon nanotube junctions: data-driven insights into structure-magnetotransport relationships
Juan Alberto Canché-Martín, Teresa Kulka, Jacek A. Majewski et al. (+3 more)
Electronic transport in carbon nanotube (CNT) assemblies is controlled by a heterogeneous population of CNT–CNT junctions, yet most microscopic studies consider only a few representative systems. Here, we construct a library of 146 single-walled carbon nanotube (SWCNT)–SWCNT junctions spanning broad structural and electronic diversity and analyse their magnetotransport using an automated workflow combining molecular dynamics, tight-binding theory, Peierls
magnetic coupling, and non-
equilibrium Green's functions.The resulting transport data are subsequently analysed using machine-learning methods. Two complementary transport descriptors reveal distinct structure–transport hierarchies. The averaged first transmission-step value is governed primarily by the mean chiral angle of the two nanotubes forming a junction, whereas the energy gap of the junction depends predominantly on the metallic or semiconducting character of the constituent CNTs. Temperature generally suppresses the averaged transmission while reducing the extracted gap, whereas a perpendicular
magnetic field affects transmission much more strongly than the gap. Signatures of interference-driven transport remain visible even at $300~\mathrm{K}$. Notably, semiconducting–semiconducting junctions retain the largest gaps but, once shifted into their conducting regime, can exhibit transmission comparable to or exceeding that of metallic junctions. These results establish statistically robust junction-level trends that can inform future network-scale models of CNT assemblies.
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All authors Juan Alberto Canché-Martín, Teresa Kulka, Jacek A. Majewski, Irina V. Lebedeva, Maciej Marchwiany, Karolina Z. Milowska
Materials Science · Cross-listed from physics.plasm-ph
Equation of state and transport coefficients of warm dense aluminum from mixed deterministic-stochastic density functional theory
Zi Li, Weijie Li, Cong Wang et al. (+2 more)
Aluminum is a reference standard in high-energy-density research and serves as a liner material in megampere Z-pinch facilities. Using mixed deterministic-
stochastic finite-temperature density functional theory, we compute the equation of state and transport coefficients of
liquid aluminum up to temperatures of 1000 eV and compare the results with model-based approaches. We find that for T<200 eV the density-functional results differ from the models by more than 10% at high density, with a maximum deviation of over 30% (at T = 10 eV), leading to significant discrepancies in the Hugoniot curve at high compression; the calculated electrical and thermal conductivities deviate from model predictions by 26% to 63% at T~100 eV. We further employ the Drude model and the Epperlein-Haines framework to examine the
magnetic-field dependence of the conductivities. These results can provide valuable input data for radiation-hydrodynamics codes.
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All authors Zi Li, Weijie Li, Cong Wang, Ping Zhang, Xianjue Peng
Mesoscale and Nanoscale Physics
Quantum heat transport and effects of quantum thermal devices in noncommuting coupled spins
Yitian Chen, Junran Kong, Huan Liu et al. (+1 more)
Quantum heat transport governs energy exchange processes and statistical laws in non-
equilibrium quantum systems, and plays a pivotal role in
quantum thermodynamics. We investigate the steady-state thermal transport of a noncommuting coupled
spin system. We employ the
quantum dressed master equation approach within the framework of open
quantum system theory to accurately analyze the non-
equilibrium dynamics, ensuring the validity of transport results in the strong coupling regime. Our results demonstrate that noncommuting
spin coupling serves as a significant resource for modulating the nonlinearity of the heat current. Specifically, in the weak
spin-coupling regime, the system exhibits robust negative differential thermal conductance (NDTC) across various
spin numbers. By deriving analytical expressions for the heat current in both the single-
spin and large-
spin limits, we reveal that this NDTC behavior is governed by microscopic cycle fluxes. Physically, this arises because
spin excitation channels induced by the cold reservoir are suppressed under a large temperature bias, thereby blocking energy exchange cycles. Conversely, in the strong
spin-coupling and large temperature bias regime, the
quantum system demonstrates pronounced thermal rectification. This high rectification efficiency originates from the unidirectional saturation of the heat current, rendering the system a promising candidate for high-performance thermal diodes. Furthermore, we extend the model to a three-terminal configuration to construct a
quantum thermal transistor. By manipulating the temperature of the gate reservoir, we achieve efficient modulation and amplification of heat flow between the source and drain. The heat amplification factor is shown to far exceed unity in specific operating regions, confirming significant thermal amplification.
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All authors Yitian Chen, Junran Kong, Huan Liu, Chen Wang
Soft Condensed Matter
Diffusion of charged rods across 3D varying section channels
N. Ray, A. Semkiv, J. Harting et al. (+1 more)
We analyze the transport of rod-like particles by
diffusion and drift in a three-dimensional channel with varying circular or elliptic cross section. Applying the Fick-Jacobs approximation to the transport equation of the particles' probability distribution, we derive an effective one-dimensional substitute model and the associated free energy profile. Our results show that the data for the mean first passage time of rods, once expressed as a function of the effective free energy barrier, collapse onto the same master curve as obtained for point or spherical particles. The observed universality provides a simple framework for predicting transport times of anisotropic particles in confined geometries without resolving the full multidimensional dynamics.
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All authors N. Ray, A. Semkiv, J. Harting, P. Malgaretti
Soft Condensed Matter
Speed up of passive tracers in mixtures with active chemical reactions
Filipe C. Thewes, Chengjie Luo and David Zwicker
Diffusivity of passive tracers in complex mixtures is widely relevant for industrial applications and for probing biological systems. Interactions with the surrounding medium typically generate a drag force that suppresses tracer
diffusion, although self-propulsion can accelerate tracers via active fluctuations. Similar effects are not understood in mixtures with particle conversion and exchange, although these are particularly relevant in biological contexts, where actively driven reactions prevail. By studying a thermodynamically consistent model of chemical reactions in mixtures, we show that reactions provide an additional relaxation pathway that suppresses interaction-induced
memory, reducing the drag on tracers and restoring their diffusivity toward the value expected in the absence of solutes. Moreover, active reactions generate nonequilibrium fluctuations that can push tracer diffusivity beyond this limit, an effect we confirm with particle-based simulations. Our results identify chemical activity as a distinct route to controlling mass transport and offer a framework for interpreting microrheology experiments in chemically active mixtures.
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Strongly Correlated Electrons
Thermal quasi-Devil's staircase in an anisotropic triangular-lattice Rydberg array
Jinghao Cao, Siyi Yang, Jingya Wang et al. (+2 more)
A Devil's staircase is a sequence of transitions between topological sectors as a control parameter is varied. Such staircases are predicted in frustrated magnets and
lattice gauge theories, but observing them is hard: the winding number that labels each sector is topologically protected, so local
quantum dynamics alone cannot move the system from one step to the next. Here we propose and analyze an experimentally feasible way to realize a thermal quasi-Devil's staircase in a finite Rydberg-atom array. We study the anisotropic triangular-
lattice Ising antiferromagnet using a dimer mapping, a directed-string description, exact thermodynamics, and Monte Carlo simulations. In the defect-free string
manifold, the commensurate–incommensurate onset follows from a simple energy–
entropy balance, and the exact Ising critical relation reduces to the same condition when triangle-rule defects are rare. On a finite
lattice, this onset appears as a quasi-Devil's staircase of winding-sector crossovers, which we resolve through winding distributions, structure factors, and directional correlations. The key point is that thermal fluctuations overcome the topological barriers that block sector changes under purely
quantum dynamics, and the staircase exists precisely at the finite sizes and tunable effective temperatures of current Rydberg platforms. This makes the effect directly observable in existing experiments. Our comparison also shows that the finite-size steps are not phase transitions: in the thermodynamic limit only a single phase transition survives, and the system crosses over to a defect-dominated paramagnet.
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All authors Jinghao Cao, Siyi Yang, Jingya Wang, Dong-Xu Liu, Zheng Yan
Materials Science
Hamiltonian learning reveals optoelectronic mechanisms across thermodynamic state space in soft semiconductors
Frederik Vonhoff, Jesper R. Pedersen, Frederico P. Delgado et al. (+5 more)
Predicting optoelectronic response across thermodynamic state space requires coupling finite-temperature nuclear dynamics to electronic structure at scales where direct first-principles calculations are impractical. Machine-learning force fields and
Hamiltonian-learning models provide scalable predictions, but integrating them into reliable and interpretable workflows remains challenging. Here, we introduce FLOW-OTTER, a modular, model-agnostic framework that automates molecular dynamics,
Hamiltonian prediction, observable extraction, reliability assessment, and
Hamiltonian-level interpretation. We demonstrate FLOW-OTTER in halide perovskites, soft
semiconductors whose anharmonic fluctuations strongly modulate electronic response. Using FLOW-OTTER, we show that independently learned nuclear and electronic models remain predictive when composed end-to-end, reproducing experimental temperature- and pressure-dependent band-gap trends using models trained only on first-principles targets at zero pressure. By resolving the nonlinear
evolution of Pb-$s$/Br-$p$ antibonding at the valence-band maximum, it identifies the microscopic origin of the asymmetric pressure response. FLOW-OTTER thus establishes
Hamiltonian learning as a general route from thermodynamic trajectories to experimentally grounded optoelectronic mechanisms.
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All authors Frederik Vonhoff, Jesper R. Pedersen, Frederico P. Delgado, Martin Schwade, Peter Beck, Jonas A. Oldenstaedt, Ivano E. Castelli, David A. Egger
Superconductivity
Superconductivity in structurally complex $\sigma$-Phase Re-X (X = V, Nb, Ta) and a derived medium-entropy alloys
Pavan Kumar Meena and Tomasz Klimczuk
The structurally complex tetragonal sigma ($\sigma$)-phase provides a unique platform for investigating the interplay between chemical disorder, electronic structure, and superconductivity, particularly in Re-based
alloys where unconventional superconductivity has been widely discussed. Here, we synthesize and investigate the superconducting properties of $\sigma$-phase Re-X (X = V, Nb, and Ta)
alloys with compositions Re$_{0.76}$V$_{0.24}$, Re$_{0.56}$Nb$_{0.44}$, and Re$_{0.60}$Ta$_{0.40}$. These compositions lie within the narrow stability range of the $\sigma$ phase, underscoring the critical role of valence electron concentration in phase formation. To examine the influence of enhanced chemical disorder, we further synthesize the structurally complex medium-
entropy alloy Re$_{0.56}$Nb$_{0.19}$Ta$_{0.19}$V$_{0.06}$, derived from these binary systems. Magnetization, electrical resistivity, and specific-heat measurements establish bulk type-II superconductivity in all compounds. Analysis of the electronic heat capacity is consistent with a fully gapped, weak-coupling BCS superconducting state. In contrast, the normal-state resistivity exhibits an unconventional negative temperature coefficient, and the superconducting transition temperature values obtained from resistivity measurements are higher than those determined from other measurements. Our results demonstrate that both the $\sigma$-phase Re-X
alloys, spanning 3d, 4d, and 5d transition-metal substitutions, and their medium-
entropy counterpart constitute an attractive family of model systems for investigating the effects of structural complexity, chemical disorder, and
spin-orbit coupling on superconductivity in Re-based materials.
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Materials Science
Combining physical models with dynamically acquired experimental information for the optimization of multicomponent NASICON fast ionic conductors in a self-driving laboratory
Bernardus Rendy, Yuxing Fei, Tanjin He et al. (+9 more)
Elemental substitution within existing structural frameworks is a widely applied strategy for developing advanced materials. Yet, optimizing target properties while maintaining phase purity usually demands extensive trial-and-error, which becomes substantially inefficient when navigating a complex design space. Here, we introduce a strategy that simultaneously and dynamically assesses composition-dependent synthetic accessibility and target properties via aggregated cost functions that guide autonomous experimentation in a truly self-driving and self-learning mode. Specifically, we developed a cost-guided autonomous solid-state synthesis (CASS) framework and demonstrate its application in the discovery of Na superionic conductor (NASICON) solid electrolytes. CASS successfully optimizes ionic conductivity and phase purity, leading to the identification of 18 promising compositions in 78 trials conducted in an autonomous laboratory, the A-Lab. Among these, we identified two fast-conducting NASICONs yielding total (bulk) ionic conductivity of 0.7 (3.96) and 0.3 (3.17) mS/cm. The successful deployment of CASS reinforces the potential of coupling self-driving autonomous laboratories with physics-informed generative models to accelerate materials discovery. Moreover, the interpretability of the design factors, informed by outcomes from both successful and failed syntheses, enables model refinement and generation of new chemical insights.
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All authors Bernardus Rendy, Yuxing Fei, Tanjin He, Xiaochen Yang, Andrea Giunto, Lauren N. Walters, David Milsted, Hao Qiu, Matthew J. McDermott, Bin Ouyang, Yan Zeng, Gerbrand Ceder
Statistical Mechanics
Two temperature scales in the Ising model on the $\{5,4\}$ hyperbolic lattice with free boundaries: susceptibility peak and boundary-induced order
Sebastian Jaroszewicz, Nahuel Mendez, Maria P. Beccar-Varela et al. (+1 more)
On the $\{5,4\}$
hyperbolic lattice, the outermost generation holds 73% of the sites at all system sizes, making macroscopic averages strictly boundary-dependent. We study the ferromagnetic Ising model on this geometry with free boundaries by Monte Carlo simulation, demonstrating that conventional observables cease to identify a single critical scale. Instead, the finite
lattices are organized by two distinct temperature scales. The susceptibility maximum identifies the lower transition scale at $T_{c2}=1.4782(15)J/k_{B}$ without extrapolation. However, the order-parameter distribution lacks a conventional fixed point at this scale. A distinct pseudocritical scale emerges instead at $T^{*}\simeq1.67(3)$ inside the boundary-sensitive intermediate phase, where Binder cumulant curves cross and effective exponents are compatible with mean-field criticality. Between $T_{c2}$ and $T^{*}$, the interior amplifies boundary fluctuations into induced order. Furthermore, because the volume grows exponentially with depth, finite-size scaling must be formulated in the generation index rather than the total number of sites. The lack of asymptotic power-law convergence in the scaling stretch confirms through an independent observable that $T^{*}$ is a finite-size crossover rather than a thermodynamic fixed point. Finally, by applying a coherent field to the outermost generation alone, we recover the upper thermodynamic transition at $T_{pt}=2.81(1)J/k_{B}$, demonstrating that it remains accessible under an appropriate boundary perturbation.
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All authors Sebastian Jaroszewicz, Nahuel Mendez, Maria P. Beccar-Varela, Maria C. Mariani
Strongly Correlated Electrons · Cross-listed from physics.chem-ph
Full-frequency GW from Cayley-transformed self-energy moments
Marcus K. Allen and George H. Booth
The dynamical GW self-energy approximation is a key computational tool to provide the fundamental spectrum of electronic systems. We reformulate this approximation, representing the particle and hole parts of the GW self-energy through a highly compact set of Cayley-transformed moment constraints. The Cayley transformation maps real frequencies to the unit circle, keeping the moments bounded as their order increases, ensuring numerical stability and allowing resolution to be focused on an energy range of interest. We calculate these Cayley-transformed moments via an efficient O[N$^4$] scaling contour integration, and from them, construct a Hermitian upfolded
Hamiltonian with a linearly scaling dimensionality with system size. A single-shot diagonalization of this effective
Hamiltonian gives an explicit full-frequency G0W0 Green's function with manifestly real poles and non-negative spectral weights. This enables quasiparticle energies, satellite features, and their spectral weights to be obtained across the full G0W0 spectrum. Comparisons with exact G0W0 calculations and convergence across the GW100 test set and the larger Chlorophyll A molecule demonstrate substantially faster and more reliable convergence with moment order than an earlier monomial-moment approach. These Cayley moment representations therefore provide a stable, compact, and systematically improvable route to the complete spectral information of zero-temperature GW, without explicit frequency grids, plasmon-pole models and other common approximations, or analytic continuation.
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Superconductivity
Nodal Orbital-Anti-Phase Superconducting State in Bilayer Nickelates
Marius Scholten, Steffen Bötzel, Frank Lechermann et al. (+2 more)
The recent discovery of high-$T_c$ superconductivity in the bilayer nickelate La$_3$Ni$_2$O$_7$ (La-327) under applied pressure and compressive strain opened a new avenue to elucidate the interplay between multiorbital intralayer and interlayer electronically driven Cooper-pairing in bilayer systems. Depending on the details of the electronic structure in the normal state, the superconducting gap in bilayer nickelates is predicted to have either bonding-antibonding $s_{\pm}$-wave
symmetry, driven by dominant interlayer Cooper-pairing, or $d$-wave
symmetry with substantial intralayer Cooper-pairing. Despite this general picture, the orbital structure of the superconducting gap in these multiorbital systems has been less explored. Here, we analyze the consequences of an orbital-anti-phase structure of the superconducting gap and discuss its possible experimental signatures. We demonstrate that additional pairs of nodes may appear on the $\alpha$ and/or $\beta$ Fermi surface sheets due to the sign change of the superconducting gap between the involved orbitals. Apart from this additional nodal structure, which is not enforced by the
symmetries of the gap function and can be probed in ARPES experiments, the orbital-anti-phase gap modifies the temperature dependence of the superfluid stiffness at low temperatures, providing a concrete experimental prediction to test its realization in bilayer nickelates and related multiorbital systems.
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All authors Marius Scholten, Steffen Bötzel, Frank Lechermann, Rafael M. Fernandes, Ilya M. Eremin
Materials Science
Rational Design of Low-Dimensional Hybrid Organic/Inorganic Interfaces for Enhanced Second-Harmonic Generation
Michele Guerrini, Muhammad Sufyan Ramzan and Caterina Cocchi
Hybrid interfaces formed by push-pull organic molecules physisorbed on two-dimensional (2D)
semiconductors provide a structurally tunable platform for engineering second-harmonic generation (SHG). However, predicting and optimizing their macroscopic response remains a formidable challenge due to the phase-sensitive interference between the nonlinear responses of the adlayer and substrate. Here, we develop a physics-informed computational screening framework that decomposes the effective second-order susceptibility into its constituent substrate, molecular, and electric-field-induced SHG channels. Validated by fully atomistic first-principles calculations across representative interface structures, this model maps the complete orientation-resolved tensor landscape of chemically modulated carbon-conjugated polar molecules on 2D substrates with distinct
symmetry. Crucially, our findings dismantle the conventional reliance on static polar descriptors, demonstrating that the ground-state permanent dipole magnitude is a fundamentally unreliable proxy for macroscopic nonlinear response. Instead, we show that the ultimate criterion for SHG maximization is encoded in the phase-resolved projection of the full anisotropic molecular hyperpolarizability tensor. On non-centrosymmetric substrates, the coherent interference between the physisorbed adlayer and the underlying 2D
matrix induces a characteristic Fano-like asymmetry and ranking reversals that are entirely absent on centrosymmetric platforms. By establishing that functionalization
topology, dynamic spatial orientation, and substrate point-group
symmetry constitute a single, non-separable parameter space, this work provides a systematic blueprint for the rational assembly, predictive discovery, and non-invasive characterization of next-generation low-dimensional hybrid materials for nonlinear optoelectronics.
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Superconductivity
Superconducting spin valve as a sensitive probe of spin-orbit coupling anisotropy
Pablo Tuero, Andreas Costa, Maria Varela et al. (+3 more)
Spin-orbit coupling (SOC) plays a central role in modern condensed matter physics and is crucial for the development of
spin-based devices and
quantum technologies. In particular, the interplay between Rashba SOC (R-SOC), arising from structural inversion asymmetry, and Dresselhaus SOC (D-SOC), due to bulk inversion asymmetry, significantly influences
spin coherence and manipulation in two-dimensional and topological systems. Disentangling these SOC components is essential for spintronics, superconducting spintronics, or topological superconductivity. In this study, we experimentally investigate in-plane low-bias conductance anisotropy in epitaxial Fe/MgO/V/MgO/Fe/Co junctions under varying temperature and
magnetic field conditions. By applying a theoretical model that accounts for distinct R-SOC and D-SOC contributions, we interpret the observed anisotropy as a reliable method to disentangle these effects. Comparison between experiment and theory reveals a 5 % contribution of D-SOC to total SOC, attributed to periodic interfacial
lattice mismatch defects confirmed by high-resolution scanning transmission electron microscopy (STEM). Our findings offer a practical approach to isolate interfacial SOC components in superconducting spintronic systems with implications for engineering in spintronic and
quantum devices, and provide further evidence of superconducting
spin-triplet pairing in Fe/MgO/V-based
superconductor/ferromagnet
heterostructures.
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All authors Pablo Tuero, Andreas Costa, Maria Varela, Yuan Lu, Jaroslav Fabian, Farkhad G. Aliev
Strongly Correlated Electrons
Mixed-Valent Magnetism in CeFe$_2$ from Multi-Impurity DFT+DMFT
Basile Herzog, Vladislav Borisov and Olle Eriksson
The microscopic origin of magnetism in CeFe$_2$ has remained unresolved for almost forty years, where polarized-
neutron diffraction and x-ray
magnetic circular dichroism infer markedly different Ce $4f$
spin and orbital moments, that also are in disagreement with theory. We show here that within a relativistic multi-impurity DFT+DMFT framework, where the Fe $3d$ states are treated by
spin-polarized T-
matrix fluctuation exchange and Ce $4f$ orbitals by a bath-coupled configuration-interaction solver, this long standing problem is resolved. This level of theory is exclusive in reproducing
magnetic moments (
spin and orbital) for both the Ce and Fe atoms, yielding a total moment in agreement with the measured saturation moment. The theory put forth here is much closer to the atom specific moments reported from XMCD, compared to values from polarized-
neutron diffraction. The occupation $\langle n_f\rangle=0.85$ and charge variance $\delta n_f^2=0.27$ establish substantial valence fluctuations, while the spectral function simultaneously recovers significant weight at the Fermi level together with separate incoherent structures. These results identify bath-mediated polarization and configuration mixing as the essential ingredients governing the electronic structure and magnetism of CeFe$_2$.
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Mesoscale and Nanoscale Physics
Valley Berry curvature dipole induced nonlinear valley Hall effect
Lulu Xiong, Xue-Jin Zhang, Zeying Zhang et al. (+4 more)
Valley Hall effect is a signature effect in the field of valleytronics, and recent studies have pushed this effect into the nonlinear regime. Here, we reveal a previously unexplored type of nonlinear valley Hall effect which arises from a valley Berry
curvature dipole (vBCD) mechanism. We show this nonlinear valley Hall effect is forbidden for conventional time-reversal-connected valleys, but is supported in the class of valleytronic systems featuring time-reversal-invariant valleys. The candidate layer groups and detailed
symmetry constraints on vBCD are obtained. It shows the nonlinear valley Hall response, as well as the nonlinear charge Hall response, can be well controlled by tuning the driving field direction. We demonstrate our proposal in an effective model study and in a concrete material example, strained Nb$_{3}$SBr$_{7}$, by first-principles calculations. The nonlocal transport signature of this vBCD induced nonlinear valley Hall effect is also discussed.
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All authors Lulu Xiong, Xue-Jin Zhang, Zeying Zhang, Yinning Zhou, Jin Cao, Cong Xiao, Shengyuan A. Yang
Statistical Mechanics
Eigenoperator Entanglement Statistics in Local Lindbladians
Ze-Kai Hong, Xu Feng and Zhi-Cheng Yang
Random
matrix spectral statistics are widely used to diagnose
quantum chaos in open systems, but whether chaotic
eigenvalue correlations are accompanied by Haar-typical eigenoperators remains unclear. We study the operator-
entanglement statistics of Liouvillian eigenoperators with near-maximal
entanglement, analogous to states near the middle of the spectrum in
Hamiltonian systems. Using the Kullback-Leibler divergence, we show that Haar-random statistics accurately describe both the Ginibre and class-AI$^\dagger$ Gaussian ensembles. For purely dissipative random Lindbladians, we find that locality of the jump operators drastically alters the eigenoperator-
entanglement statistics. Nonlocal Lindbladians remain relatively close to Haar-random behavior, whereas local Lindbladians deviate increasingly from random-
matrix statistics with system size. Moreover, unlike in
Hamiltonian systems, the most highly entangled eigenoperators of local Lindbladians do not generally lie in the region of largest density of states, owing to the clustered structure of the complex eigenspectrum. We introduce an iterative $\sigma$-clipping scheme to extract the high-
entanglement distribution without preselecting a spectral window, and find that it is Gaussian for nonlocal Lindbladians but log-normal for local ones. Remarkably, the same log-normal distribution, with no additional fitting, also describes dissipative mixed-field Ising chains belonging to distinct non-Hermitian
symmetry classes. Our results therefore point to a universal eigenoperator-
entanglement distribution for local Lindbladians that is not captured by generic non-Hermitian random-
matrix ensembles.
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Statistical Mechanics
Multidimensional dynamical centrality from Green functions in complex networks
Yusen Wang and Hao Yu
Conventional centrality measures provide compact descriptions of node importance, but they emphasize specific structural relations and do not directly resolve the temporal and spectral organization of dynamical perturbation responses. Building on the Green function of a linearized networked system, we develop a multidimensional framework for dynamical node characterization. From the same response function, we extract three complementary indicators—Influence, Efficiency, and Distortion—that quantify cumulative response strength, temporal rate of response, and spectral concentration, respectively, together with a contribution
matrix that resolves these quantities into source–target pathways. As a numerical demonstration, we apply the framework to weighted Kuramoto–Sakaguchi dynamics on heterogeneous Barabási–Albert networks. The three indicators distinguish implanted dynamical node classes through complementary dimensions of the perturbation response, while remaining strongly coupled to conventional topological centralities. These results demonstrate how a common dynamical response can be decomposed into distinct, physically interpretable characteristics rather than represented by a single aggregate descriptor. We finally discuss the scope and limitations of the linear-response assumption and extensions to time-dependent and nonlinear regimes.
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